1. Field of the Invention
The present invention generally relates to a link beam joint that is utilized in a structure that is subject to seismic loads. In particular, the link beam joint is a link-fuse joint that lengthens dynamic periods and reduces the forces that must be resisted within shear wall or frame construction of structures so that the walls or frames can withstand seismic activity without sustaining significant damage.
2. Description of the Related Art
Structures have been constructed, and are being constructed daily, in areas subject to seismic activity. Special considerations must be given to the design of such structures. In addition to normal loading conditions, the walls and frames of these structures must be designed not only to accommodate normal loading conditions, but also those loading conditions that are unique to seismic activity. For example, link beams within shear walls are typically subject to cyclic motions during seismic events. To withstand such loading conditions, structures subject to seismic activity must behave with ductility to allow for the dissipation of energy under those extreme loads.
In conventional systems, reinforced link beams subject to seismic loads have been designed with the beams fully connected directly to reinforced concrete shear walls with fully developed reinforcing bars. These beams are designed to elastically resist service wind and frequent earthquake events and are designed to plastically perform or hinge during severe earthquake events.
Since link beam length-to-depth ratios are relatively small, shear will typically control the behavior of the beams. For large shear forces, diagonal reinforcement arranged in elevation in the shape of an “X” is typically required. In other cases where shear forces are large, embedded structural steel members are placed within the reinforced concrete beams to resist the load. In all cases, these beams are designed to permanently deform in a severe seismic event. Reinforcing bars and structural steel, if used permanently, deform and concrete cracks or spalls. Energy is dissipated and beams act with ductility but plastically deform with conventional designs.
In steel braced frames, steel beams located between braces are designed to fuse during extreme seismic events. The behavior is similar to beam links used in eccentrically braced frames. These beams are designed to yield and plastically deform, protecting the bracing members and columns and the overall integrity of the structure.
Although current link beam designs may be able to withstand a seismic event, the damage caused by the joints' inability to function elastically, raises serious questions about whether conventional structures can remain in service after enduring seismic events. A need therefore exists for shear wall and steel braced frame structures that can withstand a seismic event without experiencing significant beam or joint failure, so that the integrity of the structure remains relatively undisturbed even after being subject to seismic activity.